The Central Dogma of Biology - whereby genetic information gets replicated, transcribed, and translated into proteins-is carried out by a handful of critical enzymes that include polymerases, helicases, and ribosomes. Together, these enzymes constitute a core group of sophisticated, biomolecular machines Understanding their function holds a key to understanding life, and by extension, to the treatment of human disease. Hard-won knowledge about biomolecules is informing work at the forefront of nanoscience,: which hopes to harness tiny devices to better the human condition. Put simply, we need to know how Nature's machines work if we're ever to fix them or to emulate them. A property shared by many nucleic acid-based enzymes is that they function as molecular motors: once bound to DNA or RNA, they undergo repeated cycles, often traveling considerable distances. This motion is accompanied by force production and requires chemical energy. In contrast tomechanoenzymes like myosin, the properties of nucleic acid-based motors axe modulated by an ever-changing template underfoot, yielding rich behavior. Although structural data are available for many such enzymes, comparatively little is known about their molecular mechanisms Recently, biophysical studies have been revolutionized by the ability to measure forces and displacements at the level of single molecules, using techniques that include optical traps, nanometry, and fluorescence Single-molecule approaches supply critical information that has been hitherto inaccessible by traditional techniques. Previously, my group succeeded in developing optical trapping instrumentation that?s able to register displacements down to the atomic level (~1 A). Consequently, we can record from bacterial RNA polymerase (RNAP) molecules as these step from base to base along DNA. Improved instrumental stability now allows us to reconstruct energy landscapes for folding transitions in nucleic acids that form complex structures (riboswitches, ribozymes, etc.). We propose to continue our single-molecule work on transcription by RNAP. We also plan to use single-molecule assays to address unsolved problems of co-transcriptional folding and gene regulation, and to better understand the sequence elements that regulate transcriptional elongation and termination {e.g., riboswitches). A closely related assay will allow us to study the initiation of translation by ribosomes in eukaryotes, along with the RNA sequence elements that modulate that process. Finally, we will pursue a successful single-molecule assay we developed for transcription by Pol II (RNAPII), the eukaryotic analog of RNAP.